The increasing need to conserve energy has brought an increasing demand for changeable signs and display devices which can provide an effective visual display while using as little power as possible. Modern reflective materials can replace and have often replaced illuminated power-consuming elements, such as electrical light bulbs, for many purposes. However, even where reflective changeable surfaces are used and no power is consumed to produce the actual illumination, considerable power may be required for changing or shifting a display, e.g., as in animated signs. Widely used time and temperature indicating devices, highway control panels, and the like often utilize reflective surfaces but display changing equipment is still costly to operate. A recently developed system described in The Christian Science Monitor, Apr. 19, 1973, makes use in a sign of a large number of individual rotatable elements all of which can be remotely controlled by manual, mechanical or computer means for changeable displays. See also "Signs of the Times," October 1974, pp. 48-50.
The present invention has some similarities to those described. It particularly relates to an improved system which also uses interchangeable rotatable visual elements in interchangeable modules each of which is designed to display a selected character with minimal consumption of power. The actual lighting (light-emitting or light-reflecting, etc.) surfaces which show may be of various types such as self-luminous phosphorescent, fluorescent, or merely reflective, and of various shapes and characteristics, as will be explained more fully below. Method aspects of the present invention relate to its unusual economy combined with high quality display characteristics.